Twin row drop generator

ABSTRACT

A drop generator in which two rows of orifices are formed in an orifice plate to cause two rows of drops to be generated from a single drop generating head. The drops pass through two corresponding rows of charge rings and then pass on opposite sides of an electrically conductive strip which, in cooperation with other elements of the generator, provides an electrostatic deflecting field to deflect charged drops into drop catchers. Electrically conductive plates can be utilized in conjunction with the conductive strip to set up the deflecting field or the drop catchers can be used for this purpose.

United States Patent Mathis [4 1 Oct. 31, 1972 [54] TWIN ROW DROP GENERATOR 7 3,577,198 5/1971 Beam ..346/75 [72] Inventor: gag l chflhgothe Primary ExaminerJoseph W. Hartary I p Attorney-Lawrence B. Biebel et-al. [73] Assignee: The Mead Corporation, Dayton,

- Ohio [57] ABSTRACT v I [22] Filed: Oct. 14, 1971 A drop generator in which two rows of orifices are formed in an orifice plate to cause two rows of drops [2!] Appl' 189398 to be generated from a single drop generating head. The drops pass through two corresponding rows of [52] U.S. Cl. ..346/75, 239/15, 317/3 s rings and then P on p t sides of [51 Int. Cl. ..G01d 1s/1s' electrically conductive strip which, in cc s a [58] Field of Search "346/75, 140. 317/3; 239/3, with other elements of the generator, provides an elec- 239/15 trostatic deflecting field to deflect charged drops into i drop catchers. Electrically conductive plates can be utilized in conjunction with the conductive 'strip to set [5 6] References Cited up the deflecting field or the drop catchers can be UNITED STATES PATENTS I used for this purpose.

3,404,221 10/1968 Loughren.....'.......-....346/75 X I I v 1 3 Claims, 4 Drawing Figures PAIENTEDncm I 12 3.701.998

SHEET 1 OF 2' INVENTOR GARLAND V. MATH I S A TTORNE Y8 1 'rwm Row DROP GENERATOR CROSS-REFERENCE TO RELATED APPLICATIONS BACKGROUND OF THE'INVENTION This invention relatesgenerally to the field of fluid drop generation and the application thereof to jet drop recorders ofthe type shown in Sweet et al .U.S. Pat. No. 3,373,437 and Taylor et al U.S. Pat. No. 3,560,641. In recorders of this type there are one or more rows oforifices which receive an electrically conductive, recording fluid, such as for instance a water base ink, from a pressurized fluid supply manifold and eject the fluid in rows of parallel streams. These recorders accomplish graphic reproduction by selectively charging and deflecting the drops in each of the streams and thereafter depositing at least some of the drops on a moving web of paper or other material.

The above mentioned charging is accomplished by application of control signals to charging electrodes positioned near-each of the streams. As each drop breaks off from its parent fluid filament, it carries with it a charge which is in effect a sample of the voltage present on the associated charge electrodeat the instant of drop separation. Thereafter the drop passes through an electrostatic field and is deflected in the field direction a distance which is proportional to the magnitude of the drop charge. In a preferred embodiment the drops are charged binarily for print-no-print operation; some drops being uncharged and undeflected for printing, and all other drops being charged to a fixed level and deflected into a catcher.

Additional patents of interest in this field are U.S. Pat.. Nos. 2,573,143 to Jacob and 3,404,221 to Loughren. In the Jacob patent outward deflecting and I catching ofdrops is shown while in the patent to Loughren alternate polarity deflection field plates are utilized-Generally, however, when a plurality of rows of drops are to be projected a corresponding number of drop generating heads are provided.

SUMMARY OF THE INVENTION above noted related applications, although control can also be obtained in other ways as, for example, in the manner described in the above noted patent to Taylor.

trical charge to thestrip and additional members positioned outwardly of the curtains of drops, electrostatic BRIEF DESCRIPTION OF THE DRAWINGS i FIG. 1 is an exploded perspective view of a recording head assembly; FIG. l-A. is a perspective view of a portion of the assembly of FIG. 1; n

FIG. 2 is a cross-section view through the assembly of FIG. 1;

FIG. 3 is a somewhat schematic representation of one embodiment of an electrical circuit; and g FIG. 4 is a second embodiment of an electriccircuit.'

DESCRIPTION OF THE PREFERRED EMBODIMENTS I With reference to FIG. 1 of the drawings it will be seen that the various elements of a head assembly 10 are assembled for support by a support bar 12, Assembly thereto isaccomplished by attaching the elements by means of machine screws (not shown) to a clamp bar 14 which is in turn connected to the support. bar 12 by means of clamp rods 16. I

The recording head comprises an orifice plate 18 soldered, welded or otherwise bonded to fluid supply manifold 20 with a pair of wedge-shaped acoustical dampers 22 therebetween. Orifice plate 18 is preferably formed of a relatively stiff material such as stainless steel or nickel coated beryllium-cooper but is relatively thin to provide the required flexibility for direct contact stimulation. Preferably dampers 22 are cast in place by pouring polyurethane rubber or other An electrically conductive strip is positioned downstream of the charge rings in a position such that the drops falling from each row of orifices which, in effect, form two curtains of drops, fall on opposite sides of the electrically conductive strip. By applying an elecsuitable damping material through openings 24 while tilting manifold 20 (orifice plate 18 being attached),at an appropriate angle from the vertical. This is a two step operation as dampers 22 require tilting in opposite directions (See FIG. l-A).

Orifice plate 18 contains two rows of orifices 26 and is preferably stimulated by a stimulator 28 which is threaded into clamp bar 14 to carry a stimulation probe 30 through the manifold 20 and into direct contact with plate 18. Orifice plate 18, manifold 20, clamp bar 14 together with a filter plate 32 and 0 rings 34, 36 and 38 (see also FIG. 2) comprise a clean package which may be preassembled and kept closed to prevent dirt or foreign material from reaching and clogging orifices 26. Conduit 40 may be provided for flushing of the clean package. Service connections for the recording head include a coating fluid supply tube 42, air exhaust and inlet tubes 44 and 46, and a tube 48 for connection to a pressure transducer (not shown).

. Other major elements comprising the recording head are a charge ring plate 50, an electrically conductive deflection ribbon 52 and a pair of catchers 54. Catchers 54 are supported by holders 56 which are fastened directly to fluid supply manifold 20. Spacers 58 and 60 reach through apertures 62 and 64, respectively in charge ring plate 50 to support holders 56 without stressing or constraining charge ring plate 50. Deflection ribbon 52 is also supported by holders 56 and is' stretched tightly therebetween by means of tightening block 66. Ribbon 52 extends between catchers 54 as best shown in FIG. 2.

Catchers 54 are laterally adjustable relative to ribbon 52. This adjustability is accomplished by assembling the head with catchers 54 resting in slots 68 of holders 56, and urging them mutually inward with a pair of elastic bands 70. Adjusting blocks 72 are inserted upwardly through recesses 74and 76 to bear against faces 78 of catchers54, andadjusting screws 80 are provided to drive adjusting blocks 72 and catchers 54 outwardly against elastic bands 70. Holders 56 are made of insulativematerial which maybe. any available reinforced plastic board. j I g l The fully assembled recordinghead is shown in cross section in FIG. 2. As therein illustrated coating fluid 82 flows downwardly through orifices 26 forming two rows of streams which break up into two curtains of drops 84., Drops 84 then pass through two rows of charge rings 86 in charge ring plate 50 and thence into one of the catchers 54 or onto the moving web of paper 88. Switching of drops between catch and deposit trajectories is accomplished by electrostatic charging and deflection as hereinafter described. Coordinated printing capability is achieved by staggering the two rows of streams in accordance with the teachings of Taylor et al U.S. Pat. No. 3,560,64l.'As taught in that patent, the drops in the forward row of streams (i.e. the row most advanced in the direction of web movement) are switched in a time reference frame delayed from that of the rear row by a time d/V where d is the row spacing and V is the web speed. This produces a coherence such that the two rows of streams function as a single row with an effective stream spacing equal to half the actual spacing in either of the real rows.

Formation of drops 84 is closely controlled by application of a constant frequency, controlled amplitude, stimulatingdisturbance to each of the fluid streams emanating from orifice plate 18. Disturbances for this purpose may be set up by operating transducer 28 to 'vitrate probe 30 at constant amplitude and frequency against plate 18. This cuases a continuing series of bending waves to travel the length of plate 18; each wave producing a drop stimulating disturbance each time it passes one of the orifices 26. Dampers 22 prevent reflection and repropagation of these waves. Accordingly each stream comprises an unbroken fluid filament and a series of uniformly sized and regularly spaced drops all in accordance with the well known Rayleigh jet break-up phenomenon.

As each drop 84 is formed it is exposed to the charging influence of one of the charge rings 86. If the drop is to be deflected and caught, an electrical charge is applied'to the associated charge ring 86 during the instant of drop formation. This causes an electrical charge to be induced in the tip of the fluid filament and carried away by the drop. As the drop traverses the deflecting field set up between ribbon 52 and the face of the adjacent catcher it is deflected to strike and run down the face of the catcher, where it is ingested, and carried off. Dropingestion may be promoted by application of a suitable vacuum to the ends 90 of catchers 54. When drops which are to deposit on the web 88, no electrical charge is applied to the associated charge rings. V

Appropriate charges for accomplishment of the above mentioned drop charging are induced by setting up an electrical potential difference between orifice plate 18 (or any other conductive structure in electrical contact withthe coating fluid supply) and each appropriate charge ring 86. These potential differences are created by grounding plate 18 and applying appropriately timed voltage pulses to wires 92 in connectors 94 (only one connector illustrated). Connectors 94 are plugged into receptacles 96 at the edge of charge ring plate 50 and deliver the mentioned voltage pulses over printed circuit lines 98 to chargerings 86.:

Charge ring plate 50 is fabricated from. insulative material and charge rings 86 are'merely coating of conductive material lining the surfaces of orificesin the charge ring plate. Voltagepulses for the above purpose may be generated by circuits of the type disclosed in Taylor et al, and wires 92 receiving these pulses may be matched with charge rings 86 on a one-to-one basis. Alternatively the voltage pulses may be multiplexed to decrease the number of wires and connectors. For such an alternative embodiment solid state demultiplexing circuits may be employed to demultiplex the signals and route the pulses to the proper charge rings. Such solid state circuits maybe manufacture'd'by known methods as a permanent part of charge ring plate 50.

Deflection of those drops 84 which are to be caught is accomplished by setting up appropriate electrical fields between deflection ribbon 52 and each of the catchers 54. The preferred arrangement for this function is shown in FIG. 3 wherein catchers 54 and one side of an electrical potential source 51 are all'connected to a common ground. The other side of source 51 is connected to deflection ribbon 52 thereby setting up a pair of equal strength, oppositely directed electrical deflection fields. As illustrated in FIG. 3 with the ground at the positive side of source 51, it is necessary that drops 84 be charged negatively in order-to be caught. However, it is also possible to obtain mutual outward deflection of the two curtains of drops 84 by charging the drops positively and reversing the terminals on source 51.

An alternative electrical arrangement for mutual outward deflection of the two falling drop curtains is shown in FIG. 4. As shown therein, drops 84a are charged positively, while drops 84b are charged negatively. Accordingly, two potential sources 51a and 51b are connected as illustrated to make catcher 54a negative relative to catcher 54b with deflection ribbon 52 at a potential midway between. This creates a pair of equal strength, common direction electrical flelds which cause drops 84:; to be deflected toward catcher 54a and drops 84b to be deflected toward catcher 54b. In this arrangement catchers 54a and 54b must be electrically isolated from ground and from each other, but deflection gum ribbon 52 may be grounded as shown.

The printing head as above described is adapted to be employed in combination with another such head further in accordance with the teachings of Taylor et al. Such a combination will produce solid printing coverage with the streams in each row on 16 mil centers, which is within the state of theart for current orifice plate and charge ring plate manufacturing techniques. The effective stream spacing for the equivalent single row is 4 mils, and this will produce solid printing coverage if each drop makes a printed dot in the order of about 5 mils. Suitable drops for such printed dots may be produced with 1.5 mil orifices, a fluid pressure of about 11 p.s.i.--and a stimulation frequency of about 60 KHZ. To achieve similar solid coverage in the direction of web travel the speed of web 88 should be set at about 1,200 ft. per sec.

Unexpectedly it has been found that solid printing coverage may be obtained by operating a single printing head as above described but at a reduced web travel speed. In particular, a web speed of about 450 ft. per sec. has been found to be satisfactory. This reduction in web speed results in a decreased longitudinal (i.e. web movement direction) spacing of drop deposit points. In fact when two consecutive drops in one stream are both deposited they tend to pile up and spread in all directions. They behave much like one drop of larger volume, and they fill the laterally adjacent marking cell left empty by omission of the second recording head.

This, of course, degrades the resolution of the resulting print, but a recording head has been saved. For operation in such a mode it is necessary to slow down the rate of the input drop switching data for avoidance of dimensional scaling distortion in the longitudinal direction. Thus a signal which would cause catching of (or permit deposition of) one drop in the faster two head system is stretched to catch on the average about 2.7 drops in the single head system. Catching or deposition of a single drop is not meaningful for the above mentioned single head recorder unless it is desired to make gray scale reproductions as taught for instance in Sweet et al US. Pat. No. 3,373,437.

While the form of apparatus herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the invention.

What is claimed is:

l. A multiple channel jet drop marking head comprising:

a. an orifice plate including means defining two substantially parallel rows of orifices,

b. means for supplying marking fluid to said orifices and producing at their exits parallel rows of fluid filaments,

c. a charging plate spaced from said orifice plate and having means defining parallel rows of apertures in register with said orifices for passage therethrough of said marking fluid filaments,

d. said apertures being electrically insulated from one another and each aperture being provided with-means for individually controlling electrical charging of said filaments,

e. means for stimulating said fluid filaments to break up into spaced curtains of drops corresponding to said rows of orifices, each of said curtains comprising closely spaced trains of uniformly sized and regularly spaced drops corresponding to the orifices in each of said rows thereof, the charge on each drop being determined by the charge condition of the parent fluid filament at the instant of drop separation therefrom, f. electrically conductive strip means positioned downstream of said charging plate intermediate the rows'of apertures therein between said drop curtains,

. means cooperating with said strip means to bound said drop curtains and set up therebetween electrical fields whereby the drops in said curtains are selectively deflected outwardly away from said strip means in accordance with the electrical charges thereon, and

h. means for catching drops deflected outwardly therefrom more than some predetermined distance.

2. The apparatus of claim 1 wherein;

a. said means cooperating with said strip means to set 

1. A multiple channel jet drop marking head comprising: a. an orifice plate including means defining two substantially parallel rows of orifices, b. means for supplying marking fluid to said orifices and producing at their exits parallel rows of fluid filaments, c. a charging plate spaced from said orifice plate and having means defining parallel rows of apertures in register with said orifices for passage therethrough of said marking fluid filaments, d. said apertures being electrically insulated from one another and each aperture being provided with means for individually controlling electrical charging of said filaments, e. means for stimulating said fluid filaments to break up into spaced curtains of drops corresponding to said rows of orifices, each of said curtains comprising closely spaced trains of uniformly sized and regularly spaced drops corresponding to the orifices in each of said rows thereof, the charge on each drop being determined by the charge condition of the parent fluid filament at the instant of drop separation therefrom, f. electrically conductive strip means positioned downstream of said charging plate intermediate the rows of apertures therein between said drop curtains, g. means cooperating with said strip means to bound said drop curtains and set up therebetween electrical fields whereby the drops in said curtains are selectively deflected outwardly away from said strip means in accordance with the electrical charges thereon, and h. means for catching drops deflected outwardly therefrom more than some predetermined distance.
 2. The apparatus of claim 1 wherein: a. said means cooperating with said strip means to set up electrical fields comprises opposed faces of said drop catching means.
 3. The apparatus of claim 1 wherein said means for bounding said drop curtains and setting up said electrical fields comprises: a. a pair of electrically conductive surfaces connected to a common ground and arranged parallel to said conductive strip on opposite sides thereof, and b. means for establishing said conductive strip at an electrical potential differing from the potential of said ground. 